G40 is the code for Shanghai – Shaanxi National Expressway. It starts from Shanghai and run about 1500 km and goes from about 31.23°N, 121.5°E to 34.27°N, 108.9°E. That is almost one time zone difference (15 degree).
It is pretty handy to get back to Wendy’s home town Nanyang from Shanghai. Along the way, we started from G42 and went across G15 and G2 in Shanghai, G25 and G3 in Nanjing, G35 in the middle of no where and G45 near east of Xinyang, G4 at Xinyang and finally G55 in Nanyang. That is basically the traverse of the China National Highway System.
This shows the benefit of consistent naming convention. You just need to follow on route to get to somewhere far away. Just keep driving and driving.
It also replace the original G312, just as I-40 replaced US66, the story Cars was telling. We have the same feeling. The exit to G313 was everywhere along the road. G312 goes right across the towns while G40 just bypass them.